Definitions of some new stratigraphic units in Western Venezuela
Las Pilas, Cocuiza, Vergel, El Jebe, Tres Esquinas and Nazaret. [1]

By R. M. Stainforth[2]

As an outcome of the First Venezuelan Petroleum Congress held in Caracas in March, 1962 a committee of geologists has prepared a new stratigraphic chart of Venezuela. Representatives of Creole Petroleum Corp.: Richmond Exploration Co. and Cía Shell de Venezuela were responsible for the introduction of certain new names, and the purpose of the present article is to define six of these new terms and thus validate them in advance of publication of the chart. The units in question have all received some degree of mention in the literature but, for one reason or another, were never given acceptable names.

LAS PILAS MEMBER of Querales Formation, North‑Central Falcón

The Querales Formation in the Cumarebo area and the District of Democracia has been recognized to consist of an upper sand member, named the Las Lomas, and a lower shale member, hitherto unnamed (see Léxico, p. 539). In private Creole reports recognition of this lower member can be traced back to 1925 (F. Hodson et al.), but a type section was not designated until 1950 (by J. H. Pantín). The name Las Pilas was ap­plied to it in 1952 (by H. H. Cross’. The following description of the unit is based on Pantín’s report.

Type section:  The type section of the Las Pilas Member is in  the valley of Río Querales between the northern slope of Cerro Oliva and the  southern slope of Cerro Los Tres Picos, approximately 5 kilometers northwest of the  village of Agua Clara in the District of Miranda, State of Falcón

Name:              The name Las Pilas is taken from a nearby settlement situated 300 meters south of Quebrada Querales and 2.7 kilometers upstream from its junction with Río Mitare.

Lithology:        The member or consists of approximately 92% blue‑gray to green‑gray shales and 8% medium to fine grained, silty, light gray, brown weathering sandstones. A coarse grained to conglomeratic sandstone bed, 8 meters thick, with cross laminations and ripple marks, occurs at the base.

Thickness:       The member is 574 meters thick at the type locality and thins to the east and north.

Contacts:        The contact with the underlying Cerro Pelado Formation is placed at the base of the above described 8‑meter bed of conglomeratic sandstone. This is the first prominent coarse textured sandstone encountered above the thick shales and typ­ically fine grained sandstones of the Agua Clara and Cerro Pelado Formations. This lower contact is apparently conformable although the conglomeratic and cross‑laminated character of the basal bed might indicate a local break in the depositional sequence. The contact with the upper or Las Lornas Member of the Querales Formation is readily recognizable in the field and is placed at the base of a sandstone unit 37 meters thick, which forms a prominent ridge and dip slope about 200 meters south of Quebrada Querales

Age:                 The Querales Formation, hence the Las Pilas Member, is correlated with parts of the Socorro and Pozón Formations and is of late Lower or early Middle Miocene age,

COCUIZA and VERGEL MEMBERS of San Gregorio Formation, Western Falcón

The San Gregorio Formation has been considered to include an upper member, the Río Seco conglomerate, and a lower portion which has hitherto been unnamed (see Léxico p. 587). This lower part consists largely of uniform siltstones, but can readily be divided into two members based on the presence of conspicuous fossil beds in the upper layers, The names Cocuiza and Vergel Members are proposed for these units, and the subdivision of the San Gregorio Formation is as follows:


(Río Seco Member


San Gregorio Formation

(Cocuiza Member

(siltstones with fossil beds)


(Vergel Member

(mainly siltstones)

The type section of the San Gregorio Formation (and of its members) is located two kilometers east of San Gregorio and one kilometer east of the Ulé‑Amuay pipeline. It extends from Ciénaga Vergeles in the direction N. 24° E. to the Río Seco syncline, a distance of 3.3 kilometers. The names Cocuiza and Vergel were first introduced to denote members in a private Creole report by J. J. Chapman (l950), from which the following descriptions were taken.

The San Gregorio Formation is correlated with the Tucupido Formation to the east. Both formations rest unconformably on Miocene beds and are assigned to the Pliocene.

Vergel Member

The Vergel Member takes its name from the settlement of Vergel situated near the southern end of the type section mentioned above. The type section of the member extends from the base of the southernmost conglomerate at Ciénaga Vergeles in the direction N. 24° E. to the base of the lowermost fossiliferous bed, a distance of 1.7 kilometers,

Lithology:        The Vergel Member is composed of approximately 85% siltstone, 5% sandstone and 10% conglomerate, with minor amounts of claystone.

Thickness:       This member is 330 meters thick at the type locality.

Contacts:        The Vergel Member is unconformable on the underlying Algodones Formation, The contact is placed at the base of the lowest conglomerate in the sequence. The conglomerates of the Vergel Member are lenticular and its lower contact therefore migrates up and down in the section, its upper contact is placed at the base of the lowest of the fossil beds which distinguish the Cocuiza Member.

Cocuiza Member

The Cocuiza Member takes its name from the Quebrada Cocuiza, 2.5 kilometers west of San Gregorio. Its type section continues along the line indicated above for 0.7 kilometers from the base of the lowest to the top of the highest fossiliferous bed.

Lithology:        The Cocuiza Member is readily distinguished from the Vergel Member by the presence of numerous conspicuous fossil beds separated by siltstones. The fos­siliferous beds are usually sandy and unconsolidated to slightly indurated, but some are coquinas with little associated sand. From nine to eighteen fossiliferous beds occur within the Cocuiza Member around San Gregorio and Algodones.

Thickness:       The Cocuiza Member is 80 meters thick at the type section.

Contacts:        The lower contact is placed at the base of the lowest bed of macrofossils and is normally gradational. The upper contact coincides with the top of the highest fossiliferous bed. Local unconformities exist within the formation and may occur at member contacts,

EL JEBE MEMBER of Codore Formation, Northern Falcón

The Léxico (p. 634) indicates that the name Taparito should not be used to de­signate the lower member of the Codore Formation, since it is a homonym of the Taparito Member of the Mostrencos Formation of Hedberg and Sass (1937, p. 98). The name El Jebe is here proposed for this lower member of the Codore Formation. This name has been used by G. Coronel in a private Shell report. The type section is located along Río Codore just east of the houses of El Jebe, 3.5 kilometers north of the El Mamón oilfield, as the article in the Léxico already points out. Lithologically it consists of light gray to mottled sandy clays and friable, yellowish to reddish brown sandstones. Thickness at the type locality is 460 meters.

On molluscan evidence all three members of the Codore Formation are assigned to the Upper Miocene.

TRES ESQUINAS MEMBER of Colón Formation, Western Venezuela

The “glauconite zone” at the base of the Colón Formation has long been recognized as a key horizon in the Cretaceous of the Maracaibo Basin and Western Lara. It is here proposed to formalize this unit as the Tres Esquinas Member of the Colón Formation. This name was first used in a private Creole report by W.W. Sharp (1957).

The proposed type locality is in Río Guaruríes, 1.5  kilometers northeast of the settlement of Tres Esquinas, which lies 4.5 kilometers north  of Zea in western Mérida. The type outcrops are beds of greenish, calcareous,  fossiliferous, sandy glauconite which overlie thinly bedded black limestones of the La  Luna Formation and underlie dark gray fissile shales of the Colón Formation. Both of  these contacts are considered to be conformable.

On Río Negro, in the Sierra de Perijá, the Tres Esquinas Member also overlies the La Luna Formation, but in this area it underlies the Socuy Limestone Member of the Colón Formation. In Distritos Mara and Maracaibo, northwest Zulia, the calcareous glauconitic sandstones grade into sandy glauconitic limestone, frequently pyritic. The Tres Esquinas Member is three meters thick at its type locality and ranges up to five meters elsewhere.

The presence of Bolivina explicata in its microfaunas suggests a late Coniacian age for the Tres Esquinas Member, and this accords with the accepted ages of the beds above and below it,

NAZARET FORMATION , Guajira Peninsula

Otto Renz (1960, p. 337) has described an unnamed formation of Upper Eocene age in the northeastern part of the Guajira Peninsula, The name Nazaret Formation is here proposed for this unit, since its description is based on outcrops in the vicinity of the village of Nazaret and no other locality is mentioned.

Renz’ brief description is freely translated as follows:

“During the Upper Eocene the sea invaded the northern part of the peninsula and transgressed along the northeastern edge of the Serranía de Macuire. Wholly marine Upper Eocene deposits are found there lying discordantly on gneiss and Cretaceous sediments.

“The best outcrops of Upper Eocene sediments are observed at 14 and 2 kilometers northwest of Nazaret and 1 kilometer northwest and 5 kilometers east of the same place.

“These sediments start with a basal conglomerate of variable thickness made up of rounded pebbles of gneiss and Cretaceous rocks, This conglomerate is followed by light brown limestones, partly sandy, containing abundant fragments of Lithothamnium, a rich fauna of larger foraminifera, and mollusks. Lenses and thin layers of rounded pebbles appear between the beds of limestone. The thickness of the limestone is from 60 to 100 meters.

“In all the outcrops the Upper Eocene sediments seem to lie unconformably below Miocene beds.”

Renz includes a small‑scale locality map (Fig. 2) and lists fossils indicative of Upper Eocene age. His description is considered adequate for defining a new for­mation, though a specific type section should be designated at some future date.


Léxico Estratigráfico de Venezuela (l956) Min. Minas e Hidrocarburos, Bol, de Geol., Pub. Esp. N° 1. (Caracas,)

HEDBERG, H. D. & SASS, L. C. (1937) : “Sinopsis de las formaciones geológicas de la parte occidental de la cuenca de Maracaibo, Venezuela,” Bol. Geol. y Min., vol. 1, Nos. 2‑3‑4, p. 75‑120 (Caracas)

RENZ, Otto (1960): “Geología de la parte sureste de la peninsula de la Guajira.” III Congr. Geol. Ven., Mem., tomo 1. p. 317-347 (Caracas)

[1] Manuscript received 30 October 1962,

[2] Geologist, Creole Petroleum Corporation, A single author is named for ease of future reference, but he is acting as spokesman for a group of geologists who discussed and agreed on the proposed terminology. They include H. M. Bolli, G. Coronel, G.J. Gaenslen, C. J. Kerez, J. G. Mendez, J. B. Miller, L,A, Nelson, A, Salvador and R. M. Stainforth.